A. Field of the Invention
This invention is in the field of tube plugs for heat exchange tubes used in heat exchangers, and particularly for tube plugs which tend to become tightly lodged in one end of a heat exchanger tube.
B. Discussion of Prior Art
This invention pertains to heat exchangers including shell and tube, air cooled, double pipe and other types. In conventional heat exchangers a plurality of heat exchange tubes are secured between opposing tubesheets with ends of the tubes tightly engaged in holes in the respective tubesheets. The ends of the heat exchange tubes are normally connected to the tubesheets using hydraulic expansion or hydraulic expansion and seal welding to achieve a fluid-tight seal intended to withstand extreme temperature and pressure changes of fluid flowing through said tubes and about the external surfaces of said tubes.
Exemplary patents in the prior art incorporated herein by reference disclose a variety of tube plugs for use with heat exchange tubes. Applicant's own co-pending published U.S. application, U.S. 2012/0118547 discloses a tube plug intended to stop fluid from accumulating at the tubesheet area and isolate this area from fluid stagnation which could result in corrosion. This tube plug includes a sealing flange at its distal end to be situated inwardly of the tubesheet.
U.S. Pat. No. 4,800,637 to Overbay discloses a tube plug inserted in a heat exchange tube mounted in a tubesheet. As seen in FIGS. 1 and 4, bolt 50 has threaded engagement with force pad 52 and extends axially to the bottom distal closed flat end of tube plug 26. When bolt 50 is rotated its distal end presses against the distal flat inside end of tube plug 26 and stretches this plug for the purpose of reducing the plug's outer diameter so that it can be more easily pulled out of the heat exchange tube 14.
U.S. Pat. No. 1,794,369 to Edgar discloses a sealing plug composed of four segments 11 forming a circular tubular structure called spool 10, which is surrounded by an asbestos sleeve 13. Also, there is a central spindle 16 extending axially through spool 10. Rotation of tapered spindle 16 in the bore formed by segments 11 of spool 10, causes the segments to displace radially outward, which presses the cylindrical sleeve 13 really outward to form a better seal with the bore surface of the plastic tube into which spool 10 is inserted.
U.S. Pat. No. 4,653,542 to Epstein discloses a tube plug 10 with a threaded bore surface 28 which receives mating threads 72 of insert 14. This insert is screwed into the proximal end of tube plug 10 at its tapered area 68 as seen in FIGS. 1, 4 and 5. The insert deflects the thin proximal end walls of tube plug 10 radially outward to press and seal against the bore surface of the heat exchange tube 24.
U.S. Pat. No. 5,944,057 to Pierce discloses a holding member 14 which has a smooth cylindrical outer surface that is driven into the central bore of tube plug 12 to expand the plug into better sealing engagement with the bore of the open end of the heat exchange tube 22.
U.S. Pat. No. 6,688,336 to Trichard discloses the concept of rotating a tube plug; however, this reference requires external threads on the tube plug to engage and cut into the bore of the plugged tube which is a relatively soft plastic, this device thus being not applicable to hard steel heat exchange tubes.
None of the above described prior art tube plugs pertain to the problem addressed by the present invention namely removal of a tube plug which is lodged, fused, wedged or otherwise bound in and with the proximal end of a heat exchange tube in a heat exchanger or furnace.
In the operation of heat exchangers, problems may occur from pin holes, cracks, clogging or other fluid seal issues in heat exchange tubes. Such tubes need to be taken out of service and isolated from the heat exchanger operation to prevent further problems with these tubes, and to allow the heat exchanger to continue operation without these defective tubes. The conventional approach is to insert a tapered solid metal plug in each of the opposite ends of a defective tube. Such a plug is forcefully driven into the open tube end until there is a fluid-tight interference fit. This kind of repair can be done in the field or elsewhere, but is intended to provide a quick and relatively inexpensive solution, with the expectation that the tube plug and defective tube may be removed at a later date and a new replacement tube installed.
The present invention pertains particularly to situations where a conventional tube plug must be removed from its installation in the end of a heat exchange tube. Due to the original interference fit, corrosion, heat changes which may be extreme and other factors during the operation of the heat exchanger, it is common for such conventional tube plugs when employed, to become so tightly lodged in the ends of the tubes that removal is extremely difficult. The current plug removal practice is by hammering the exposed plug head in left and right and up and down directions until the plug has broken free from the bore of the heat exchange tube. This procedure often enlarges and damages the tubesheet hole, so that future re-use of the tubesheet will be difficult for attachment and sealing a tube-to-tubesheet junction. Damaged tubesheet holes are difficult to repair, and replacement costs are not only expensive but require taking the entire heat exchanger out of service which impacts a much larger operation.
The present invention addresses the above-described problems as regards damage to heat exchange tubes and to tubesheets resulting from conventional removal operation of conventional tube plugs and the undesirable results in cost, down-time and inconvenience.